420 



APPENDIX 



DRAWING THE 



the two diagonals; and through that centre draw a 

 line d e, perpendicular to the edge, if the base be 

 square or rectanglar, or perpendicular to the hori- 

 zontal diagonal, if the base be a rhomb* On this 

 perpendicular, and on each side of the base, take \ 

 the length of the axis of the particular octahedron 

 we are delineating, and draw lines from the extre- 

 mities of these semi-axes, to the angles of the base. 



In the regular octahedron, which is the figure 

 above represented, the semi- axis is equal to \ the 

 diagonal of the horizontal projection of the base. 



To draw the Rhombic Dodecahedron. 

 Fig. 380. 



The easiest method of drawing this figure is to 

 project the cube as shewn above, and through its 

 centre and perpendicular to its planes, to draw the 

 lines a &, c d, ef. 



Those lineis are parallel respectively to the edges 

 of the cube. Take on each line, and in each direc- 

 tion from the point in the centre of the cube, where 

 the lines intersect each other, a quantity equal to 

 that edge of the cube to which the particular line is 

 parallel, and draw lines from the extremities of those 



